FACING THE BOSSES:
Uranus and Master - Just beat the game on the default setting, you can set the number of bouts to win to 1 to make it easier, you must get your name up for this to work. After you've done this, at the character select screen, hold Select on the '? ' to slow down the random select and wait till you see them.
Sho and Vermillion - Turn the difficulty to 5 in options then beat it with Master and there you go.

SELECTING BOSS CHARACTERS:
Uranus & Master Code:
At title screen on controller one while words are flying in hit L1, L2, Triangle, R1, R2, Square.
Sho & Vermilion Code:
At title screen on controller two while words are flying in hit Square, R2, R1, Triangle, L2, L1 (after the first code has been entered).
Remove Power Bars Code:
Pause the game while fighting then hold down X + Triangle + Square + Circle & Press Select twice.

New Moves For All Characters:
Pounce (while other player is on the ground) - L + 0
Stomp (while other player is on the ground also must be close) - 11 + X
Quick roll - fhold fand a roll button
Running moves - simply press any button while running
Four button trick - X+O+A+Cl and b or f or d to access special moves also works in the air

Miscellaneous Cheat Information:
* When random selecting it is possible to choose from more than just the two standard colour sets. Pressing each one of the four attack buttons (Triangle, Square, Circle, X) yields a different set.
* Wait for opponent to stop bouncing before a pounce or stomp move
* Pressing Select during the match performs a taunt move. (it increases your opponents special meter).
* Beat the game with either Sho or VermiIion and you can access the characters special moves with R1 + R2
* Beat the full battle mode on the highest difficulty and you can fight Vermillion.
* Select Gaia from the select screen, (it will work in either 1 or 2 player) before it says "Fight', Quickly press Up, Up, Up, Down, then about 5 pieces of armour will fly around Gaia and they will mold to his body and then you have Armoured Gaia. He takes about 1/2 normal damage but he is very slow.